Inhibitor for acid pickling baths and process of making



Patented Nov. 30, 1943 .um'rap STATES PATENT o 2,335,452 FFICE minerron FOR Adm momma rnocass or MAKING BATES AND Franz Schelling, Dornholzlmusen in Taunus,

Germany; dian N Drawing. Application No. 352,465. In Ge vested in the Alien Property Gusto- August 13, 1940. Serial rmany June 10, 1939 3 Claims. (Cl. 252-149) I froth agents may eflective'manner if the inhibitors contain condensation products of aldehydes and/or ketones and other condensable substances besides the above mentioned ammonium thiocyanate.

A condensation products according to my in.- vention I mean the well known compounds obtained by condensation of amines or their derivatives such as urea, thiourea. cyanamide, dicyandiamide or phenols and their derivatives with aldehydes, ketones and/or polymerisation products thereof. Condensation products of artificial resin character have proved to be especially suitable.

The ammonium thiocyanate used in combination with the condensation products serves 'as can'ier. 'I'hiourea, however, serves not only as carrier for the artificial resin but is also one of the components of the artificial resin itself.

Especially good results were obtained by the use of products which were formed in the heat through the action ofaldehydes and ketones on complex compounds of ammonium thiocyanate or thiourea or mixtures therefrom with aniline.

According to my invention mixtures of ammonium thiocyanate and thiourea may be produced by mechanical mixing of the components, preferably in equal parts or by heating of ammonium thiocyanate to temperatures of 150-230" 0.

Excellent results will be obtained if the process is carried out on the basis of ammonium thiocyanate or thiourea 'or their mixtures. I prefer to work in suchmanner that the condensation products are manufactured in such small quantities that they form a thin layer on the surface of the crystals of ammonium thiocyanate or thiourea.

' aniline and 3 to 8 "parts of The inhibitors made from artificial resins sometimes show the disadvantage that they agglomerate on account of their slow solubility, especially during the hot pickling on the beginning of the pickling whereby the sheets may adhere together. According to my invention this disadvantage may be prevented by adding porous substances to the inhibitors, such as wood dust, potato flour, talcum or the like, either The quantities of inhibitors to be added may vary in wide ranges. In general, additional quantities of. 0.01% are suflicient to warrant an efiicient protection of the metals against the pickling acids.

If desired, suitable wetting. emulsifying or be added to the inhibitors made from artificial resins..

Example 1 A mixture of thiourea and ammonium thiocyanate is heated to 150-230 C. to parts of this mixture are mixed with 5 to 10 parts of v paraformaldehyde and heated 6 to 20,hours at IO- C. The time of heating may be ascertained by simple pre--- heating should be liminary tests. Too long avoided, as the reaction products will otherwise become insoluble. Tothe thus obtained products 2 to 3% wood dust are added and intimately mixed. An extraordinarily eflicient non-hygroscopic inhibitor is obtained.

Example 2 86 parts of a mixture of equal parts ammo- 3 to 5 parts of sawdust, 4 parts paraformaldehyde and 10 parts aniline and the so formed mixture heated 20 hours at 80 C. Thereby a yellow artificial resin is formed on the ammonium thiocyanate and thiourea crystals respectively. This inhibitor exerts a greater inhibiting effect than the best hitherto known picklings even in very small concentrations and in hot acid. The following comparative tests prove its superiority. The comparative tests were carried out with 20% sulphuric acid; pickling time one hour. The results may be seen from the followin table:

. Without Pickling addition "Rodine according (pure pickling 1 my acid) invention 1. Addition 0.03% temp. 60:

Decrease in g./qm grs 74. 4. 52 3. Inhibiting eil'ect. per cent. 0 03. 0 06.

2. Addition 0.02% temp. 60:

. Decrease in g./qm grs 74. 6. 7 3. Inhibiting eflect per cent 0 91 95. 3. Addition 0.01% temp. 60:

Decrease in g./qm grs 74. 46 8. 6 5. Inhibiting eiiect per cent.. 0 88. 4 92. 4. Addition 0.02% temp. 80: Decrease in g.lqm .grs. 371 I 17. 26 11. Inhibiting efiect.. per cent 0 95. 35 96.

during the operative process or thereafter.

These additions produce a uniform distribution of the inhibitors in the pickling bath and cause a higher degree of efiiciency.

metals comprising at least one substance sefor acid baths for pickling lected from the group consisting of ammonium 3. A process for the preparation of an intniocyanate and thiourea the crystals or which hibitor foracid baths i'or pickling metals, which are coated superficially with a condensation comprises heating a mixture containing 75 to 85 product of paraformaldehyde and aniline. parts of a mixture of ammonium thiocyanate 2. An inhibitor for acid baths for pickling 5 and thiourea, 5 to parts of aniline, 3 to 8 metals composed of a mixture of ammonium parts of paraformaldehyde for a period of 6 to thiocyanate and thiourea the crystals of which hours at C. to C. are superficially coated with a condensation I product of paraformaldehyde and aniline. FRANZ SCHELLING. 

